Google Panda Continuous Update But Gets Prepared Between Roll Outs?

Today is the 5th anniversary of the Google Panda update, which touched down on February 24, 2011. Yesterday, John Mueller of Google answered another question on Panda, and his answer I found interesting.

How long until panda algo finishes the slow rollout? How often do you update the panda score? Is the user satisfaction with the query in search results the ultimate ranking signal for that page and site overall? Will panda update happen before penguin?

John Mueller responded:

So from what I am aware of, the Panda algorithm is rolling more or less continuously, in the sense that one update rolls out and the next update gets prepared and starts rolling out as well. So it is not that you’d see this kind of discrete point in time where you say well this was that update and that was the next update. It kind of rolling continuously. So from there, it does;’t really make sense to look at specific dates.

The interesting part is not the continuously rolling out part, that we know now. But that Google gets the " next update gets prepared" and then it rolls out also. What is Google preparing here? It is confusing, again.

I guess Panda is a continuous roll out but has some manual aspect to it? Maybe that is what it means that it is part of the core algorithm?